According to the international Dry Eye Workshop (DEWS), “dry eye” is defined as follows: “Dry eye is a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance, and tear film instability with potential damage to the ocular surface. It is accompanied by increased osmolarity of the tear film and inflammation of the ocular surface” (The Ocular Surface Vol. 5, No. 2: 75-92, 2007).
An eye drop (Chondron (registered trademark)) containing chondroitin sulfate (hereinafter may be referred to as “CS”) has been known in Japan, and the eye drop has the effect of “protecting the superficial cornea.” Studies on the effect of CS on the ocular surface (Tsutomu Fujihara, et al., Journal of Ocular Pharmacology and Therapeutics, Vol. 11, No. 4: 503-508, 1995) have reported the examination of the prevention of corneal epithelial disorders. Teruo Nishida, et al., Experimental Eye Research, 53: 753-758, 1991 describes the examination of the presence or absence of the effect of CS on corneal epithelial cells. The recent literature Gary D. Novack, The Ocular Surface, Vol. 12, No. 3: 227-230, 2014 describes a variety of therapeutic agents for dry eye developed in Japan and the U.S.
Regarding CS derivatives having a cross-linked structure through a cross-linker (hereinafter such a derivative may be referred to as “cross-linked CS”) (WO 1991/16881, pamphlet, Japanese Patent Application Laid-Open (kokai) No. 1994-73102, Amnon Sintov, et al., Biomaterials, 16: 473-478, 1995), Rubinstein, et al. have reported attempts to produce CS derivatives using 1,12-diaminododecane as a cross-linker (WO 1991/16881, pamphlet, Amnon Sintov, et al., Biomaterials, 16: 473-478, 1995). In the field of CS, CS (which is readily water-soluble) is cross-linked for imparting poor water-solubility thereto, for use as, for example, membranes or tablets.